Income Taxes - Income Tax Expense (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income Taxes [Line Items]
Current income tax expense	$ 15,709	$ 20,052
Deferred income tax benefit	(2,118)	(2,539)
Income tax expense, as reported	$ 13,591	$ 17,513
Effective tax rate	19.80%	22.30%